The present invention relates to a process for uniting superposed metal plates to one another through one or more spot welds.
Lamination of metal sheets has traditionally been done by xe2x80x9cspot weldingxe2x80x9d that is an electric resistance welding process in which the overlapping metal sheets are disposed between a pair of electrodes between which a heavy current of short duration is passed. The high electrical resistance at the interface between the two metal sheets produces significant heating, causing the metals to melt at their interface and form a localized weld in that region. This process works well for many metals, particularly for steel. However, resistance spot welding does not work well for some metals, one being aluminum. The combination of tenacious high resistance surface oxides and low melting point make the process difficult at best when applied to aluminum. Traditional spot welding is also questionable in many instances when laminating different metals.
The difficulties with laminating some types of metals lead to the development of the explosion welding technique. This is a non-fusion welding process that welds metal plates together over large surface areas. The explosion welding technology employs a high velocity collision between two metal sheets to create micro-melting and metallurgical welding across their interfaces. The collision is created by subjecting one of the plates to the detonation of a high energy granular explosive charge applied over the full plate surface. The explosion accelerates the plate across a fixed distance to collide with the second plate. The process is typically applied to the lamination of large plates where continuous surface welding is desired.
While some semblance of spot welding can be achieved with small separated charges of explosive welding, when continuous welding is not required, the process is cumbersome, expensive and environmentally challenging requiring specialized equipment and off-site facilities to accommodate the violent nature of the explosions. Explosive welding is not suitable for high volume spot welds such as are required in automotive or aircraft assembly operations. Accordingly, a simpler, more effective process of spot welding obstinate materials is needed that can be readily adapted to industrial shop conditions.
It is therefore the primary object of the present invention to provide a novel process for laminating metal plates by a process of spot welding that relies on the kinetic energy of a projectile to produce the necessary welding energy.
The novel process of the invention involves the placing of metal sheets that are to be laminated in spaced apart parallel relation, one to another. The parallel sheets are then anchored or placed against a backstop to fix the position of the inside one of the two sheets. When the location of the spot weld is determined, a projectile is fired at the outside one of the two sheets. The kinetic energy of the projectile that is transferred to the outside plate by the projectile""s impact with that plate accelerates a portion of the plate across the space between the two plates to create a high energy spot collision between the two plates that results in the plates being metallurgically welded together at the point of their impact.